1. Field of Invention
The present invention relates to a method of driving an electro-optical device, an electro-optical device and an electronic apparatus. More specifically, the invention relates to gradational control by subfield driving that uses a pixel provided therein with memories.
2. Description of Related Art
Subfield driving is a related art halftone display method. When subfield driving is used as a time axis modulation method, a predetermined period of time (for example, 1 frame as a display unit of a picture in a case of moving picture) is divided into a plurality of subfields, and pixels are driven by a combination of subfields corresponding to a gradation to be displayed. The gradation being displayed is determined in accordance with a ratio of the pixel-driving period of time as a part of a predetermined period of time. The ratio is specified by a combination of the subfields. In this method, like a amplitude modulation method, since there is no need to prepare voltages applied to electro-optical elements such as a liquid crystal, as much as the number of display gradations, the circuit scale of a driver to drive a data line can be reduced. Further, there is an advantage in that it can reduce or suppress deterioration of the display quality caused by the differences in characteristics of a D/A converter circuit or an OP amplifier or the like, or non-uniformity in various types of wire resistance or the like.
Japanese Unexamined Patent Application Publication No. 2002-082653 discloses a subfield driving in which pixels provided therein with memories are used. More particularly, each of the pixels include memory to store a plurality of bits of gradational data, and a pulse width control circuit connected to the rear stage of the memory in each of the pixels. The pulse width control circuit alternatively applies to a pixel electrode an on-voltage by which a pixel display state is set up as an on-state or an off-voltage by which a pixel display state is set up as an off-state, in accordance with data stored in a memory of the pixel. The ratio of applied time of the on-voltage that occupies 1 frame, i.e., the duty ratio is specified based on gradation data stored in a memory of the pixel. Once gradation data are written in the memory in any one of the pixels, gradational display continues in accordance with the data stored in the memory. Accordingly, in principle, with respect to a pixel in which gradation does not need to be changed, there is no need to perform writing of data again. In contrast, with respect to a pixel in which gradation needs to be changed, new gradation data are written in memories in the corresponding pixel whenever necessary.